Dry etch process

ABSTRACT

A method for conformal dry etch of a liner material in a high aspect ratio trench is achieved by depositing or forming an inhomogeneous passivation layer which is thicker near the opening of a trench bat thinner deep within the trench. The methods described herein use a selective etch following formation of the inhomogeneous passivation layer. The selective etch etches liner material faster than the passivation material. The inhomogeneous passivation layer suppresses the etch rate of the selective etch near the top of the trench (where it would otherwise be fastest) and gives the etch a head start deeper in the trench (where it would otherwise be slowest). This method may also find utility in removing bulk material uniformly from within a trench.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/724,767 by Zhang et al, filed Nov. 9, 2012, and titled “DRY ETCH PROCESS.” This application also claims the benefit of U.S. Provisional Application No. 61/732,074 by Kim et al, filed Nov. 30, 2012 and titled “DRY-ETCH FOR SELECTIVE OXIDATION REMOVAL.” Each of the above U.S. Provisional Applications is incorporated herein in its entirety for ah purposes.

BACKGROUND OF THE INVENTION

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.

Dry etch processes are often desirable for selectively removing material from semiconductor substrates. The desirability stems from the ability to gently remove material from miniature structures with minimal physical disturbance. Dry etch processes also allow the etch rate to be abruptly stopped by removing the gas phase reagents. Some dry-etch processes involve the exposure of a substrate to remote plasma by-products formed from one or more precursors. For example, remote plasma excitation of ammonia and nitrogen trifluoride enables silicon oxide to be selectively removed from a patterned substrate when the plasma, effluents are flowed into the substrate processing region. Remote plasma etch processes have recently been developed to selectively remove a variety of dielectrics relative to one another. However, fewer dry-etch processes have been developed to evenly and selectively remove metals and/or their oxidation.

Methods are needed to evenly and selectively etch oxidation layers from metal surfaces using dry etch processes.

BRIEF SUMMARY OF THE INVENTION

A method for conformal dry etch of a liner material in a high aspect ratio trench is achieved by depositing or forming an inhomogeneous passivation layer which is thicker near the opening of a trench but thinner deep within the trench. The methods described herein use a selective etch following formation of the inhomogeneous passivation layer. The selective etch etches liner material faster than the passivation material. The inhomogeneous passivation layer suppresses the etch rate of the selective etch near the top of the trench (where it would otherwise be fastest) and gives the etch a head start deeper in the trench (where it would otherwise be slowest). This method may also find utility in removing bulk material uniformly from within a trench.

Embodiments of the invention include methods of etching material from a high aspect ratio trench on a patterned substrate. The methods include the sequential steps of (1) providing a patterned substrate having a conformal liner layer on walls of the high aspect ratio trench, and (2) forming an inhomogeneous passivation layer over the conformal liner layer in the high aspect ratio trench. The inhomogeneous passivation layer has an outer passivation thickness near the opening of the high aspect ratio trench which is greater than an inner passivation thickness deep within the high aspect ratio trench. The sequential steps also include (3) gas phase etching the conformal liner layer. The gas phase etching process selectively removes material from the conformal liner layer faster than material from the inhomogeneous passivation layer. The sequential steps further include (4) removing the remainder of the inhomogeneous passivation layer to leave a remainder of the conformal liner layer. The remainder of the conformal liner layer has an enter remaining conformal liner thickness near the opening of the high aspect ratio trench and an inner remaining conformal liner thickness deep within the high aspect ratio trench. The outer remaining conformal liner thickness is greater than the inner remaining conformal liner thickness. The sequential steps further include (5) gas phase etching the remainder of the conformal liner layer to leave nearly vertical walls on the sides of the high aspect ratio trench.

Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of she specification or may ho learned by the practice of the disclosed embodiments. The features and advantages of the disclosed embodiments may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the invention may be realized by reference to the remaining portions of the specification and the drawings, presented below. The Figures are incorporated into the detailed description portion of the invention.

FIG. 1 is a cross-sectional schematic before and after a prior art etching of a liner material in a high aspect ratio trench.

FIG. 2 is a flowchart depicting steps of a method for conformal dry etch in a high aspect ratio trench according to embodiments of the invention.

FIG. 3 is a collection of cross-sectional schematics at several stages during the dry etch method of FIG. 2 according to embodiments of the invention.

FIG. 4A shows a substrate processing chamber according to embodiments of the invention.

FIG. 4B shows a showerhead of a substrate processing chamber according to embodiments of the invention.

FIG. 5 shows a substrate processing system according to embodiments of the invention.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference babel irrespective of the second reference label.

DETAILED DESCRIPTION OF THE INVENTION

A method for conformal dry etch of a liner material in a high aspect ratio trench is achieved by depositing or forming an inhomogeneous passivation layer which is thicker near the opening of a trench but thinner deep within the trench. The methods described herein use a selective etch following formation of the inhomogeneous passivation layer. The selective etch etches liner material raster than the passivation material. The inhomogeneous passivation layer suppresses the etch rate of the selective etch near the top of the trench (where it would otherwise be fastest) and gives the etch a head start deeper in the trench (where it would otherwise be slowest). This method may also find utility in removing bulk material uniformly from within a trench.

During gas phase etch processes, etchant precursors have been found to lose some effectiveness progressively as they diffuse deeper within a high aspect ratio trench. This results from the increased number of collisions which occur as the aspect ratio is increased. Etchant precursors have been found to lose some effectiveness progressively as they diffuse deeper within a high aspect ratio trench. This results from the increased number of collisions which occur as the aspect ratio is increased. FIG. 1 shows the result of a prior art process applied to a trench formed in a patterned substrate 100. The walls 105 of the trench are lined with a conformal liner 110-1. Since the etch rate is faster at the top of high aspect ratio trench than at the bottom, the post etch liner 110-2 displays a V shape instead of a uniform width from top to bottom as in the pre-etch condition.

This is an invention to achieve conformal etch in high aspect ratio structure in semiconductor IC fabrication. The inventors have found a new method of uniform removal of material within a high aspect ratio trench. In order to better understand and appreciate the invention, reference is now made to FIGS. 2-3. FIG. 2 is a flowchart of a conformal dry etch process sequence according to embodiments of the invention while FIG. 3 is a collection of schematics at various points during the process sequence of FIG. 2. This invention achieves conformal dry etch in high aspect ratio trench. A patterned substrate with a high aspect ratio trench is provided (operation 202). The high aspect ratio trench is formed by walls 305 which are lined with conformal liner layer 310-1 (which may or may not be the same material as the walls 305). An inhomogeneous passivation layer 320-1 is then formed (operation 204) and is thicker near the top of the trench and relatively thin deeper within the trench as shown in the second panel of FIG. 3.

After passivation (204), a selective gas phase etch is applied (operation 206). Selective gas phase etch removes conformal liner 310-1 material faster than inhomogeneous passivation layer 320-1 material. As a consequence, the presence of inhomogeneous passivation layer 320-1 increases the etch rate deep within the trench which counteracts the gas phase etches natural tendency to remove excess material at the top of the trench. The inhomogeneous passivation layer 320-1 is optionally removed in operation 208. In disclosed embodiments, the no inhomogeneous passivation layer 320-1 material remains after selective gas phase etch (operation 206) and operation 208 becomes redundant. Operation 208 is necessary especially if materials are selected such that the selective gas phase etch is highly selective of the conformal liner 310-1 material over inhomogeneous passivation layer 320-1 material.

A second gas phase etch step (operation 210) is applied to the remaining liner material 310-2. This time around, the natural tendency of the gas phase etch to etch more quickly near the opening of the trench is compensated by the fact that there is more material to etch near the opening. In this way, the compound etch described and claimed herein can uniformly remove a conformal liner at an even etch rare. The overall result is a conformal etch with similar etch amount across the depth of the trench.

In disclosed embodiments, the inhomogeneous passivation layer is formed by consuming some material from the conformal liner layer such that the conformal liner layer is thinner near the opening of the trench and thicker deep within the trench. In this embodiment, the conformal liner layer is no longer conformal following the formation of the inhomogeneous passivation layer, however, the adjective “conformal” will still be used in order to keep layer references straight.

The inner remaining conformal liner thickness may be measured within the bottom 20%, within the bottom 10%, or within the bottom 5% of the high aspect ratio trench in embodiments of the invention. Likewise, the inner passivation thickness may be measured within the bottom 20%, within the bottom 10%, or within the bottom 5% of the high aspect ratio trench. At the other end of the trench, die outer remaining conformal liner thickness may be measraed within the top 20%, within the top 10%, or within the top 5% of the high aspect ratio trench. Lastly, the outer passivation thickness may be measured within the top 20%, within the top 10%, or within the top 5% of the high aspect ratio trench indisclosed embodiments.

The inner remaining conformal liner thickness is less than or about 20%, less than or about 10%, or less than or about 5% of the outer remaining conformal liner thickness in embodiments of the invention. In some cases, the inner remaining conformal liner thickness may be close to or zero nanometers.

In embodiments, the invention described may be used for the vertical 3D NAND memories fabrication. For this semiconductor application, there are high aspect trenches in nmltiple-bilayer film stacks. Lateral and conformal etch of one material of the bilayer against the other is required. This etch process benefits the application most when it is conformal, i.e. has similar etch rate from top to bottom across the deep holes or trenches.

Generally speaking, the compensation algorithm described herein will also work for bulk materials. In such cases, the term liner layer will still be used herein, however, it will refer to the portion of the hulk material which is removed by the conformal gas phase etch process sequence. In other words, the conformal liner layer may be an outer portion of a bulk material within walls of the high aspect ratio trench in disclosed embodiments.

In one material system example, the material of the conformal liner layer to be etched is silicon (e.g. single crystal silicon, polysilicon or amorphous silicon in the form of a liner). The inhomogeneous passivation layer is silicon oxide or silicon nitride, formed by an oxygen plasma, a nitrogen plasma or a carbon plasma treatment of the silicon liner. The source of oxygen, nitrogen or carbon (e.g. O₂, NH₂, or CH₄) may be delivered to a local plasma excitation within the substrate processing region to form the inhomogeneous passivation layer of silicon oxide, silicon nitride or silicon carbide. Hybridized materials such as silicon oxynitride, silicon oxycaxbide or silicon carbon nitride may also be created to form the inhomogeneous passivation layer. In those exemplary processes, some of the silicon in the silicon layer is consumed.

In another material system example, the material of the conformal liner layer to be etched is silicon oxide and the inhomogeneous passivation layer is silicon or silicon nitride. In another material system example, the material to be etched is silicon nitride and the inhomogeneous passivation layer is silicon or silicon oxide. In another example, the material to be etched is tungsten, and the passivation layer is tungsten oxide or tungsten nitride. The conformal liner layer may also be titanium and the inhomogeneous passivation layer is either titanium oxide or titanium nitride in disclosed embodiments.

The aspect ratio of the nigh aspect ratio trenches may be greater than 10:1 (height to width), greater than 25:1, greater than 30:1, greater than 50:1, greater than 75:1 or greater than 100:1 in embodiments of the invention. As a result of the diversity of integrated circuit techniques used today, the Applicants envision considerable latitude in the absolute length scales which fall into these aspect ratio regimes. In one example, conformal etch is achieved for a high aspect ratio trench with a width of 20 nm to 50 nm and a depth of 1 μm to 2 μm. The conformal etch may be applied to a high aspect ratio trench having a depth greater than 0.5 μm, greater than 1.0 μm or greater than 2.0 μm in disclosed embodiments. The trench may have a width less than 50 nm, less than 30 nm or less than 25 nm in embodiments of the invention.

Additional process parameters are disclosed in the course of describing an exemplary processing methods and systems.

Exemplary Processing Methods and Systems

Processing chambers that may implement embodiments of the present invention may be included within processing platforms such as the CENTURA® and PRODUCER® systems, available from Applied Materials, Inc. of Santa Clara, Calif. Examples of substrate processing chambers that can be used with exemplary methods of the invention may include those shown and described in co-assigned U.S. Provisional Patent App. No. 60/803,499 to Lubomirsky et al, filed May 30, 2006, and titled “PROCESS CHAMBER FOR DIELECTRIC GAPFILL,” the entire contents of which is herein incorporated by reference for all purposes. Additional exemplary systems may include those shown and described in U.S. Pat. Nos. 6,387,207 sod 6,830,624, which are also incorporated, herein by reference for ail purposes. Selective etches with high selectivities available for a broad array of materials fund utility as the gas phase etch used herein. Chambers and processes with appropriate selectivities may be procured from Applied Materials, Santa Clara, Calif.

Generally speaking, selective etches have been created for a wide variety of inhomogeneous patterned substrates by flowing a fluorine-containing precursor through a remote plasma system or a remote plasma region in general (including the possibility of a chamber plasma region as described below). Supplementary precursors may be introduced to determine the selectivity. Supplementary precursors are either flowed through the remote plasma region or directly into the substrate processing region. The substrate temperature has also been found to be a helpful parameter for determining the selectivity. In some eases the remote plasma power level, the process pressure and the precursor flow ratios have also been used to obtain a desirable selectivity. Describing an exemplary processing chamber will help to convey the ways in which these process parameters are controlled.

FIG. 4A is a substrate processing chamber 1001 according to disclosed embodiments. A remote plasma system 1010 may process a fluorine-containing precursor and/or a secondary precursor which then travels through a gas inlet assembly 1011. Two distinct gas supply channels are visible within the gas inlet assembly 1011. A first channel 1012 carries a gas that passes through the remote plasma system 1010 (RPS), while a second channel 1013 bypasses the remote plasma system 1010. Either channel may be used for the fluorine-containing precursor, in embodiments. On the other hand, the first channel 1012 may be used for the process gas and the second channel 1013 may be used for a treatment gas. The lid (or conductive top portion) 1021 and a perforated partition 1053 are shown with an insulating ring 1024 in between, which allows an AC potential to be applied to the lid 1021 relative to perforated partition 1053. The AC potential strikes a plasma in chamber plasma region 1020. The process gas may travel through Erst channel 1012 into chamber plasma region 1020 and may be excited by a plasma in chamber plasma region 1020 alone or in combination with remote plasma system 1010. If the process gas (the fluorine-containing precursor) flows through second channel 1013, then only the chamber plasma region 1020 is used for excitation. The combination of chamber plasma region 1020 and/or remote plasma system 1010 may be referred to as a remote plasma system herein. The perforated partition (also referred to as a showerhead) 1053 separates chamber plasma region 1020 from a substrate processing region 1070 beneath showerhead 1053. Showerhead 1053 allows a plasma present in chamber plasma region 1020 to avoid directly exciting gases in substrate processing region 1070, while still allowing excited species to travel from chamber plasma region 1020 into substrate processing region 1070.

Showerhead 1053 is positioned between chamber plasma region 1020 and substrate processing region 1070 and allows plasma effluents (excited derivatives of precursors or other gases) created within remote plasma system 1010 and/or chamber plasma region 1020 to pass through, a plurality of through-holes 1056 that traverse the thickness of the plate. The showerhead 1053 also has one or more hollow volumes 1051 which can be filled with a precursor in the form of a vapor or gas (such as a silicon-containing precursor) and pass through small holes 1055 into substrate processing region 1070 but not directly into chamber plasma region 1020. Showerhead 1053 is thicker than the length of the smallest diameter 1050 of the through-holes 1056 in this disclosed embodiment. In order to maintain a significant concentration of excited species penetrating from chamber plasma region 1020 to substrate processing region 1070, the length 1026 of the smallest diameter 1050 of the through-holes may be restricted by forming larger diameter portions of through-holes 1056 part way through the showerhead 1053. The length of the smallest diameter 1050 of the through-holes 1056 may be the same order of magnitude as the smallest diameter of the through-holes 1050 or less in disclosed embodiments.

Showerhead 1053 may be configured to serve the purpose of an ion suppressor as shown in FIG. 4A. Alternatively, a separate processing chamber element may be included (not shown) which suppresses the ion concentration traveling into substrate processing region 1070. Lid 1021 and showerhead 1053 may function as a first electrode and second electrode, respectively, so that lid 1021 and showerhead 1053 may receive different electric voltages. In these configurations, electrical power (e.g., RF power) may be applied to lid 1021, showerhead 1053, or both. For example, electrical power may be applied to lid 1021 while showerhead 1053 (serving as ion suppressor) is grounded. The substrate processing system may include a RF generator that provides electrical power to the lid and/or showerhead 1053. The voltage applied to lid 1021 may facilitate a uniform distribution of plasma (i.e., reduce localized plasma) within chamber plasma region 1020. To enable the formation of a plasma in chamber plasma region 1020, insulating ring 1024 may electrically insulate lid 1021 from showerhead 1053. Insulating ring 1024 may be made from a ceramic and may have a high breakdown voltage to avoid sparking. Portions of substrate processing chamber 1001 near the capacitively-coupled plasma components just described may further include a cooling unit (not shown) that includes one or more cooling fluid channels to cool surfaces exposed to the plasma with a circulating coolant (e.g., water).

In the embodiment shown, showerhead 1053 may distribute (via through-holes 1056) process gases which contain fluorine, hydrogen and/or plasma effluents of such process gases upon excitation by a plasma in chamber plasma region 1020. In embodiments, the process gas introduced into the remote plasma system 1010 and/or chamber plasma region 1020 may contain fluorine (e.g. F₂, NF₃ or XeF₂). The process gas may also include a carrier gas such as helium, argon, nitrogen (N₂), etc. Plasma effluents may include ionized or neutral derivatives of the process gas and may also be referred to herein as radical-fluorine and/or radical-hydrogen referring to the atomic constituent of the process gas introduced.

Through-holes 1056 are configured to suppress the migration of ionically-charged species out of the chamber plasma region 1020 while allowing uncharged neutral or radical species to pass through showerhead 1053 into substrate processing region 1070. These uncharged species may include highly reactive species that are transported with less-reactive carrier gas by through-holes 1056. As noted above, the migration of ionic species by through-holes 1056 may be reduced, and in some instances completely suppressed. Controlling the amount of ionic species passing through showerhead 1053 provides increased control over the gas mixture brought into contact with, the underlying wafer substrate, which in turn increases control of the deposition and/or etch characteristics of the gas mixture. For example, adjustments in the ion concentration of the gas mixture can alter the etch selectivity (e.g., the tungsten oxide:tungsten etch ratio).

In embodiments, the number of through-holes 1056 may be between about 60 and about 2000. Through-holes 1056 may have a variety of shapes hut are most easily made round. The smallest diameter 1050 of through-holes 1056 may be between about 0.5 mm and about 20 mm or between about 1 mm and about 6 mm in disclosed embodiments. There is also latitude in choosing the cross-sectional shape of through-holes, which may be made conical, cylindrical or combinations of the two shapes. The number of small holes 1055 used to introduce unexcited precursors into substrate processing region 1070 may be between about 100 and about 5000 or between about 500 and about 2000 in different embodiments. The diameter of the small holes 1055 may be between about 0.1 mm and about 2 mm.

Through-holes 1056 may be configured to control the passage of the plasma-activated gas (i.e., the ionic, radical, and/or neutral species) through showerhead 1053. For example, the aspect ratio of the hoses (i.e., the hole diameter to length) and/or the geometry of the holes may be controlled so that the flow of ionically-charged species in the activated gas passing through showerhead 1053 is reduced. Through-holes 1056 in showerhead 1053 may include a tapered portion that faces chamber plasma region 1020, and a cylindrical portion that faces substrate processing region 1070. The cylindrical portion may be proportioned arm dimensioned to control the flow of ionic species passing into substrate processing region 1070. Art adjustable electrical bias may also be applied to showerhead 1053 as an additional means to control the how of ionic species through showerhead 1053.

Alternatively, through-holes 1056 may have a smaller inner diameter (ID) toward the top surface of showerhead 1053 and a larger ID toward the bottom surface. In addition, the bottom edge of through-holes 1056 may be chamfered to help evenly distribute the plasma effluents in substrate processing region 1070 as the plasma effluents exit the showerhead and thereby promote even distribution of the plasma effluents and precursor gases. The smaller ID may be placed at a variety of locations along through-holes 1056 and still allow showerhead 1053 to reduce the ion density within substrate processing region 1070. The reduction in ion density results from an increase in the number of collisions with walls prior to entry into substrate processing region 1070. Each collision increases the probability that an ion is neutralized by the acquisition or loss of an electron from the wall. Generally speaking, the smaller ID of through-holes 1056 may be between about 0.2 mm and about 20 mm. In other embodiments, the smaller ID may be between about 1 mm and 6 mm or between about 0.2 mm and about 5 mm. Further, aspect ratios of the through-holes 1056 (i.e., the smaller ID to hole length) may be approximately 1 to 20. The smaller ID of the through-holes may be the minimum ID found along the length of the through-holes. The cross sectional shape of through-holes 1056 may be generally cylindrical, conical, or arty combination thereof.

FIG. 4B is a bottom view of a showerhead 1053 for use with a processing chamber according to disclosed embodiments. Showerhead 1053 corresponds with the showerhead shown in FIG. 4A. Through-holes 1056 are depicted with a larger inner-diameter (ID) on the bottom of showerhead 1053 and a smaller ID at the top. Small holes 1055 are distributed substantially evenly over the surface of the showerhead, even amongst the through-holes 1056 which helps to provide more even mixing than other embodiments described herein.

An exemplary patterned substrate may be supported by a pedestal (not shown) within substrate processing region 1070 when fluorine-containing plasma effluents and oxygen-containing plasma effluents arrive through through-holes 1056 in showerhead 1053. Though substrate processing region 1070 may be equipped to support a plasma for other processes such as curing, no plasma is present during the etching of patterned substrate, in embodiments of the invention.

A plasma may be ignited either in chamber plasma region 1020 above showerhead 1053 or substrate processing region 1070 below showerhead 1053. A plasma is present in chamber plasma region 1020 to produce the radical-fluorine from an inflow of me fluorine-containing precursor. An AC voltage typically in the radio frequency (RF) range is applied between the conductive top portion (lid 1021) of the processing chamber and showerhead 1053 to ignite a plasma in chamber plasma region 1020 during deposition. An RF power supply generates a high RF frequency of 13.56 MHz but may also generate other frequencies alone or in combination with the 13.56 MHz frequency.

The top plasma may be left at low or no power when the bottom plasma in the substrate processing region 1070 is turned on to either cure a film or clean the interior surfaces bordering substrate processing region 1070. A plasma in substrate processing region 1070 is ignited by applying an AC voltage between showerhead 1053 and the pedestal or bottom of the chamber. A cleaning gas may be introduced into substrate processing region 1070 while the plasma is present.

The pedestal may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration allows the substrate temperature to be cooled or heated to maintain relatively low temperatures (from room temperature through about 120° C.). The heat exchange fluid may comprise ethylene glycol and water. The wafer support platter of the pedestal (preferably aluminum, ceramic, or a combination thereof) may also be resistively heated in order to achieve relatively high temperatures (from about 120° C. through about 1100° C.) using an embedded single-loop embedded heater element configured to make two full turns in the form of parallel concentric circles. An outer portion of the heater element may run adjacent to a perimeter of the support platter, while an inner portion runs on the path of a concentric circle having a smaller radius. The wiring to the heater element passes through the stem of the pedestal.

The chamber plasma region or a region in a remote plasma system may be referred to as a remote plasma region. In embodiments, the radical precursors (e.g. radical-fluorine and any secondary radical precursors) are formed in the remote plasma region and travel into the substrate processing region where the combination preferentially etches, for example, polysilicon, silicon oxide, silicon, nitride, titanium nitride or tungsten oxide. Plasma power may essentially be applied only to the remote plasma region, in embodiments, to ensure that the radical-fluorine and any secondary radical precursors (which together may be referred to as plasma effluents) are not further excited in the substrate processing region. Addition of an unexcited precursor (e.g. water, an alcohol or amine-containing precursor) has also proven desirable as an alternative to a secondary radical precursor in order to extend the range of gas-phase etches in selectively-space.

In embodiments employing a chamber plasma region, the excited plasma effluents are generated in a section of the substrate processing region partitioned from a deposition region. The deposition region, also known herein as the substrate processing region, is where the plasma effluents mix and react to etch the patterned substrate (e.g., a semiconductor wafer). The excited plasma effluents may also be accompanied by inert gases (in the exemplary case, argon). The substrate processing region may be described herein as “plasma-free” daring etching of the substrate. “Plasma-tree” does not necessarily mean the region is devoid of plasma. A relatively low concentration of ionized species and free electrons created within the plasma region do travel through pores (apertures) in the partition (showerhead/ion suppressor) due to the shapes and sixes of through-holes 1056. In some embodiments, there is essentially no concentration of ionized species and tree electrons within the substrate processing region. The borders of the plasma in the chamber plasma region are hard to define and may encroach upon the substrate processing region through the apertures in the showerhead. In the case of an inductively-coupled plasma, a small amount of ionization may be effected within the substrate processing region directly. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the forming film. All causes for a plasma having much lower intensity ion density than the chamber plasma region (or a remote plasma region, for that matter) during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein.

Nitrogen trifluoride (or another fluorine-containing precursor) may be flowed into chamber plasma region 1020 at rates between about 5 sccm and about 500 sccm, between about 10 sccm, and about 300 sccm, between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm in disclosed embodiments. Combined flow rates of fluorine-containing precursor and secondary precursors into the chamber may account for 0.05% to about 20% by volume of the overall gas mixture; the remainder being carrier gases. In the ease of the fluorine-containing precursor, a purge or carrier gas may be first initiated into the remote plasma region before those of the fluorine-containing gas to stabilize the pressure within the remote plasma region.

Plasma power applied to the remote plasma region can be a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma is provided by RF power delivered between lid 1021 and showerhead 1053. In an embodiment, the energy is applied using a capacitively-coupled plasma unit. When using a Frontier™ or similar system, the remote plasma source power may be between about 100 watts and about 3000 watts, between about 200 watts and about 2500 watts, between about 300 watts and about 2000 watts, or between about 500 watts and about 1500 watts in embodiments of the invention. The RF frequency applied in the exemplary processing system may be low RF frequencies less than about 200 kHz, high RF frequencies between about 10 MHz and about 15 MHz or microwave frequencies greater than or about 1 GHz in different embodiments.

Substrate processing region 1070 can be maintained at a variety of pressures during me flow of carrier gases and plasma effluents into substrate processing region 1070. The pressure within the substrate processing region is below or about 50 Torr, below or about 30 Torr, below or about 20 Torr, below or about 10 Torr or below or about 5 Torr. The pressure may be above or about 0.1 Torr, above or about 0.2 Torr, above or about 0.5 Torr or above or about 1 Torr in embodiments of the invention. Cower limits on the pressure may be combined with upper limits on the pressure to arrive at further embodiments of the invention.

In one or more embodiments, the substrate processing chamber 1001 can be integrated into a variety of multi-processing platforms, including the Producer™ GT, Centura™ AP and Endura™ platforms available from Applied Materials, Inc. located in Santa Clara, Calif. Such a processing platform is capable of performing several processing operations without breaking vacuum. Processing chambers that may implement embodiments of the present invention may include dielectric etch chambers or a variety of chemical vapor deposition chambers, among other types of chambers.

Embodiments of the deposition systems may be incorporated into larger fabrication systems for producing integrated circuit chips. FIG. 5 shows one such system 1101 of deposition, baking and caring chambers according to disclosed embodiments. In the figure, a pair of FOUPs (front opening unified pods) 1102 supply substrate substrates (e.g., 300 mm diameter wafers) that are received by robotic arms 1104 and placed into a low pressure holding areas 1106 before being placed into one of the wafer processing chambers 1108 a-f. A second robotic arm 1110 may be used to transport the substrate wafers from the low pressure holding areas 1106 to the wafer processing chambers 1108 a-f and back. Each wafer processing chamber 1108 a-f, can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein, in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation and other substrate processes.

The wafer processing chambers 1108 a-f may include one or more system components for depositing, annealing, curing and/or etching a flowable dielectric him on the substrate wafer. In one configuration, two pairs of the processing chamber (e.g., 1108 c-d and 1108 e-f) may be used to deposit dielectric material on the substrate, and the third pair of processing chambers (e.g., 1108 a-b) may be used to etch the deposited dielectric. In another configuration, all three pairs of chambers (e.g., 1108 a-f) may be configured to etch a dielectric film on the substrate. Any one or more of the processes described may be carried out on chamber(s) separated from the fabrication system shown in different embodiments.

The substrate processing system is controlled by a system controller. In an exemplary embodiment, the system controller includes a hard disk drive, a floppy disk drive and a processor. The processor contains a single-board computer (SBC), analog and digital input/output boards, interlace boards and stepper motor controller boards. Various parts of CVD system conform to the Versa Modular European (VME) standard which defines board, card cage, and corrector dimensions and types. The VME standard also defines the bus structure as having a 16-bit data bus and a 24-bit address bus.

System controller 1157 is used to control motors, valves, flow controllers, power supplies and other functions required to carry out process recipes described herein. A gas handling system 1155 may also be controlled by system controller 1157 to introduce gases to one or all of the water processing chambers 1108 a-f. System controller 1157 may rely on feedback from optical sensors to determine and adjust the position of movable mechanical assemblies in gas handling system 1155 and/or in wafer processing chambers 1108 a-f. Mechanical assemblies may include the robot, throttle valves and susceptors which are moved by motors under the control of system controller 1157.

In an exemplary embodiment, system controller 1157 includes a hard disk drive (memory), USB ports, a floppy disk drive and a processor. System controller 1157 includes analog and digital input/output hoards, interface boards and stepper motor controller boards. Various parts of multi-chamber processing system 1101 which contains substrate processing chamber 1001 are controlled by system controller 1157. The system controller executes system control software in the form of a computer program stored on computer-readable medium such as a hard disk, a floppy disk or a flash memory thumb drive. Other types of memory can also be used. The computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, RF power levels, susceptor position, and other parameters of a particular process.

A process for etching, depositing or otherwise processing a film on a substrate or a process for cleaning chamber can be implemented using a computer program product that is executed by the controller. The computer program code can be written in any conventional computer readable programming language: for example, 68000 assembly language, C, C++, Pascal, Fortran or others. Suitable program code is entered into a single file, or multiple files, using a conventional text editor, and stored or embodied in a computer usable medium, such as a memory system of the computer. If the entered code text is in a high level language, the code is compiled, and the resultant compiler code is then linked with an object code of precompiled Microsoft Windows® library routines. To execute the linked, compiled object code the system user invokes the object code, causing the computer system to load the code in memory. The CPU then reads and executes the code to perform the tasks identified in the program.

The interface between a user and the controller may be via a touch-sensitive monitor and may also include a mouse and keyboard. In one embodiment two monitors are used, one mounted in the clean room wall for the operators and the other behind the wall for the service technicians. The two monitors may simultaneously display the same information, in which case only one is configured to accept input at a time. To select a particular screen or function, the operator touches a designated area on the display screen with a finger or the mouse. The touched area changes its highlighted color, or a new menu or screen is displayed, confirming the operator's selection.

As used herein, “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon” of the patterned substrate is predominantly Si but may include minority concentrations of other elemental constituents such as nitrogen, oxygen, hydrogen, carbon and the like. Exposed “silicon nitride” of the patterned substrate is predominantly Si₃N₄ but may include minority concentrations of other elemental constituents such as oxygen, hydrogen, carbon and the like. Exposed “silicon oxide” of the patterned substrate is predominantly SiO₂ but may include minority concentrations of other elemental constituents such as nitrogen, hydrogen, carbon and the like. In some embodiments, silicon oxide films etched using the methods disclosed herein consist essentially of silicon and oxygen. “Tungsten oxide” is predominantly tungsten and oxygen but may include minority concentrations of other elemental constituents such as nitrogen, hydrogen, carbon and the like. Tungsten oxide may consist of tungsten and oxygen. “Titanium nitride” is predominantly titanium and nitrogen but may include minority concentrations of other elemental constituents such as nitrogen, hydrogen, carbon and the like. Titanium nitride may consist of titanium and nitrogen.

The term “precursor” is used to refer to any process gas which takes part in a reaction to either remove material from or deposit material onto a surface. “Plasma effluents” describe gas exiting from the chamber plasma region and entering the substrate processing region. Plasma effluents are in an “excited state” wherein at least some of the gas molecules are in vibrationally-excited, dissociated and/or ionized states. A “radical precursor” is used to describe plasma effluents (a gas in au excited state which is exiting a plasma) which participate in a reaction to either remove material from or deposit material on a surface. “Radical-fluorine” (or “radical-hydrogen” or “radical-oxygen”) are radical precursors which contain fluorine (or hydrogen) but may contain other elemental constituents. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated info a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film.

The phrase “high aspect ratio” may refer to structures like deep gaps or holes. Regardless of shape as viewed from above, all high aspect ratio structures will be referred to as “trenches” herein. The terms “gap” and “trench” are used throughout with no implication that the etched geometry has a large horizontal aspect ratio. Viewed from above the surface, trenches may appear circular, oval, polygonal, rectangular, or a variety of other shapes. A trench may be in the shape of a moat around an island of material. The term “via” is used to refer to a low aspect ratio trench (as viewed from above) which may or may not be filled with metal to form a vertical electrical connection. As used herein, a conformal etch process refers to a generally uniform removal of material on a surface in the same shape as the surface, i.e., the surface of the etched layer and the pre-etch surface are generally parallel. A person having ordinary skill in the art will recognize that the etched interlace likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances.

Having disclosed several embodiments, it will be recognised by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups. 

What is claimed is:
 1. A method of etching material from a high aspect ratio trench on a patterned substrate, the method comprising the sequential steps of: providing a patterned substrate having a conformal liner layer on walls of the high aspect ratio trench; forming an inhomogeneous passivation layer over the conformal liner layer in the high aspect ratio trench, wherein the inhomogeneous passivation layer has an outer passivation thickness near the opening of the high aspect ratio trench and an inner passivation thickness deep within the high aspect ratio trench, and wherein the outer passivation thickness is greater than the inner passivation thickness; gas phase etching the conformal liner layer, wherein the gas phase etching process selectively removes material from the conformal liner layer faster than material from the inhomogeneous passivation layer; removing the remainder of the inhomogeneous passivation layer to leave a remainder of the conformal liner layer, wherein the remainder of the conformal liner layer has an outer remaining conformal liner thickness near the opening of the high aspect ratio trench and an inner remaining conformal liner thickness deep within the high aspect ratio trench, and wherein the outer remaining conformal liner thickness is greater than the inner remaining conformal liner thickness; gas phase etching the remainder of the conformal liner layer to leave nearly vertical wails on the sides of the high, aspect ratio trench.
 2. The method of claim 1 wherein an aspect ratio of the high aspect ratio trench may be greater than 10:1.
 3. The method of claim 1 wherein the inner passivation thickness is less than or about 20% of the outer passivation thickness.
 4. The method of claim 1 wherein the inner remaining conformal liner thickness is less than or about 20% of the outer remaining conformai liner thickness.
 5. The method of claim 1 wherein the inner remaining conformal liner thickness is measured within the bottom 20% of the high aspect ratio trench.
 6. The method of claim 1 wherein the inner passivation thickness is measured within the bottom 20% of the high aspect ratio trench.
 7. The method of claim 1 wherein the outer remaining conformal liner thickness is measured within the top 20% of the high aspect ratio trench.
 8. The method of claim 1 wherein the outer passivation thickness is measured within the top 20% of the high aspect ratio trench.
 9. The method of claim 1 wherein the inhomogeneous passivation layer is formed by consuming some material from the conformal liner layer such that the conformal liner layer is thinner near the opening of the trench and thicker deep within the trench.
 10. The method of claim 1 wherein the conformal liner layer is single crystal silicon, polysilicon or amorphous silicon.
 11. The method of claim 1 wherein the inhomogeneous passivation layer is silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, silicon oxycaxbide or silicon carbon nitride.
 12. The method of claim 1 wherein the conformal liner layer is silicon oxide and the inhomogeneous passivation layer is silicon nitride or silicon.
 13. The method of claim 1 wherein the conformal liner layer is silicon nitride and the inhomogeneous passivation layer is silicon oxide or silicon.
 14. The method of claim 1 wherein the eonforrnal liner layer is tungsten and the inhomogeneous passivation layer is tungsten oxide or tungsten nitride.
 15. The method of claim 1 wherein the eonforrnal liner layer is titanium and the inhomogeneous passivation layer is titanium oxide or titanium nitride.
 16. The method of claim 1 wherein the eonforrnal liner layer is an outer portion of a bulk material within walls of the high aspect ratio trench.
 17. The method of claim 1 wherein the high aspect ratio trench has a depth greater than 0.5 μm. 